View Full Version : Belts & pulleys,

28-09-2012, 05:25 PM
my next build is going to use belts and pulleys for all axis', I'm going to use a range of gear sizes so I'm just wondering, I'll probably run it 28:28 teeth for the moment.

how much adjustment should the the stepper motors need to keep the belts taught? what distance between the ball screw and the stepper motor is a good distance.

It a bit of an awkward question but I hope someone gets it :)


28-09-2012, 05:59 PM
The distance between the pulleys for a given belt length is easy to calculate, or you can use an online calculator such as this one (http://www.sdp-si.com/cd/default.htm). However slight manufacturing variations in the belt length and possibly the need to put the belt on without stretching means you always need some adjustment to ensure the correct tension can be obtained in the belt. If you have a few mm adjustment of the centre distance, either side of the calculated value, that should be plenty. I like to incorporate much more adjustment so that you can change the ratio, e.g. from 1:1 to 1:2, without having to change the belt.

Since you seem to have opted for 1:1 the centre distance doesn't make a lot of difference as the belt will wrap round 180 of the pulley regardless. I'd just use whatever fits nicely with the rest of the design, which will probably end up being around 100-150mm.

Bearing station (http://www.bearingstation.co.uk/products/Pulleys/HTD_Pulleys/HTD_Pulley_5mm) are the cheapest place to get the timing belts and HTD pulleys and second cheapest are belting online (http://www.beltingonline.com/timing-pulleys-272/htd5-pulleys-285/) by the time you include their VAT and higher postage charge. I did just recently find a local shop (http://www.bearingcentre.org.uk/) who are cheaper than both of these companies, plus of course no postage and waiting around, so might be worth checking if there's somewhere near you?

28-09-2012, 10:49 PM
thanks jon, another question though

what size drag chain would you recomend? I'm thinking 25x38 or 18x38.

it will only be for two steppers using YY cable, spindle coolant, spindle also using YY and a general coolant pipe.

and I'm going to use a Alu plate for my Z axis with the rails on the spindle side like yours, there will only be 200mm of travel.

would you reccomend using thicker then 10mm?


28-09-2012, 11:40 PM
Pass on the drag chain, just look at the diameters of all the cables and tubes you need to get through it and get whichever size will fit with some room to spare...

Most people use CY not YY cable since YY lacks shielding which helps protect other items from electromagnetic interference.

Generally 20mm plate is used since you don't gain much by using thicker plate and 10mm is certainly too thin. Also if you can get the bearings drawn in red further down, closer to the bed, that will reduce the overhang and make the axis stronger.

29-09-2012, 12:32 AM
silly me, I only flipped the rails earlier so I hadn't actually got to moving them down :)

I already use CY, just forgot the name!

cool anyway, I'll just make it thicker.